Explosion proof acoustic device



July 24, 1956 A. L. PITTINGER 2,756,281

EXPLOSION PROOF ACOUSTIC DEVICE 2 Sheets-Sheet 2 Original Filed May 5, 1949 FIG; 3

INVENTOR ABRAHAM L. PITTINGER BY fiwm United States Patent- O EXPLOSIONPROOF ACOUSTIC DEVICE" Abraham L. Pittinger, Pasadena, Calif.-'

Original application May 3, 1949, Serial No. 91,207, now

Pate'nf'No. 2,655,566, datedOc'to'ber 13, 1953. D vide'd and"'fl1is'"applicatibn'April "21, 1953, Serial N0.

'Z-Claims. (Cl. 179-1155 (Granted under Title 35,11. Si'Code (1952),sec. 266) This invention relates to transducers and more pan ticularly to a new and improved construction thereof; The present invention has particular application .to sealed transducers of the explosion proof type for use in hazard-. ous areas. This application is a division of'copending application Serial No. 91,207, filedMayS, 1949, now Patent Number 2,6555 66.

In the design of apparatus-for usein mines powder magazines and similar installations Where .the atmosphere may be laden with dangerous gases, dust,' vaporsor liquids it-is important that all electrical elements be shielded so .that in the event there is any sparking in. .the electrical system, the resultingsflame will. be confined within the electrical instrument :andcannot spread to the surrounding atmosphere; The problem of making such installations explosion proof without interfering. with the eflic'iency or operation of such equipment is, of course, an-extremely important considerations With the advent of public address systems "in. factories, warehouses,'etc., a particular problemthas .arisen in connection withflthe design of loudspeakers forsuchsystems especially-where the devices are to beusedin industries where the aforementioned hazardous conditions aretpreseat.

The conventional phenolic diaphragmspeakers do not meet the rigid safety requirementsfor such-installations This is true even through the electrical eelments mayrbe mounted in a closed speaker housing with the peripheral. edge of the speaker cone insealed engagement with the housing to provide an airtight construction. Since the diaphragrmmust of necessity'be of relativelydight material, on the order of 3 to 5-thousandthsof an inch in thickness, there is always danger that the diaphragm maycrack' and thus admit-gases into the area surrounding the electrical elements. If this shouldoccur any" sparks-developing in the electrical elements-could 5 spread the-flameto the surrounding atmosphere andset ofi an explosion.

The present invention may be used with particular advantage 'in overcoming the dangers and defects inherent in the conventional loudspeakers for such use and may be installed with complete safety regardless of the fact that the surrounding atmosphere may be laden with gases or substances of an explosive nature.

It is an object of the present invention to provide a sealed transducer.

A second object is to provide a novel linkage between the acoustical and electrical elements of a transducer.

Still another object of the present invention is to combine a sealed construction with a novel linkage adapted to operate through such sealing arrangement.

An additional object is the provision of an explosion proof transducer which may be used With safety under harbardous conditions.

A further object is the provision of means for automatically sealing off a portion of the transducer at the instant an explosion occurs.

These and other objects and attendant advantages will "ice 21f; be readily apparent: from the following description taken in conjunction withthe accompanying drawings 'in which:

Fig. l :is :an axial sectionalview illustrating one embodiment of. the present invention;-,

Fig. 2 is a fragmentary view similar. to Fig.1 illustrating-.a modified'form'of the presentinvention; and

Fig.3 is a view similar to .Figs; 1 and 2 and showing a modification permitting the operating parts: to be spaced apart a substantial distance..

Referring now to the drawings wherein like reference characters referntoidentical; parts the present invention isdisclosed-in connection with its application to the permanent magnet type of loudspeakers. In the embodiment shown inFigs. land-2 the. permanent magnet may comprisecylinder l0 of Alnicoi or other suitable material-positioned in thecavity-of a nonferrous cup-shaped housing-11 'witha-softiron disc 12 contacting theupper end of the cylinder 10 and extending over the openend of: the housing I ,1 1 toprovide a closure therefor. This disc.1.2..may be suitably secured in-sealed-relationto a flanged face 13--on housing 111 to prevent the entrance of dirt, gases .ormoistureintothe housing cavity. A soft iron core 14-maybe aflixedtto disc :as by Welding onother well. known .means. so that .the core .depends downwardly intothe housing ca-vity and -is positioned centrally of .theFAlnico" cylinder tbores A second soft iron disc 15 resting,on-anrannular ledge-.16 in the-lower. portionio the housing and in contact Withthelower end of-Alnico .cylinderthas acentral-aperture to providea :magnetic fluxgap 17-adjacent the lower end of core 14 thereby completing ,the magnetic field.

Referring now-especiallyto Fig. 1 it will be notedthat avoicecoilhldis mounted on aflexiblebellows 19: with the coil positioned in .the fluxgap. The bellows may be .av sylphon bellows or a flexible diaphragm of the aneroid .type and, in .theembodiment illustrated, one end.

of thebellowsis secured to thelower .end of .core 14 as by threaded-bushing 19a and-its. other end is secured by scnew-20 or. other .suitable-.-means to v0ice:coil carrying cup, 21. An axial bore. 22.. extendingv longitudinally through core 14 connects thehollow interior 'of the aforementioned bellows with ansimilar fiexible bellows 23 afiixedto the uppenend of. theliron core member. A

speakerscone 24=supported at its rim byspeaker casing.

25 may be attached .atxits-center to the upper bellows unit-23hr afiangednut 26 as illustrated. Ascan be seen the-hollow interiorof the upper and lower flexible bellows-membersthe bore provide a closed chamber betweentthewvoice. coil and the speaker cone. This. chamber maybefilledflwithna fluid such as auhydraulic: oil: onagasrandsealed. This .fluid-thenrprovides the con-.- necting linkage betweeni-voiceucoiln18 and .speaker'cone. 24. Thus, as the electrical impulses energize the voice coil and impart movement thereto, the fluid in the chamber will transmit the movement to the speaker cone where it is translated into sound waves.

The eelctrical wires connecting the voice coil in circuit with the source of electrical energy may enter the housing through an explosion proof conduit connection including a circular disc 27 of insulating material having a pair of binding posts 28 extending therethrough so that the desired connections can be made to the posts on each side of the disc. This disc may be clamped be tween an internal ledge 29 in the threaded opening of the housing and the end of a threaded conduit coupling 30 thus providing a seal at the conduit connection.

As illustrated a valve plunger 31 may be mounted so as to project upwardly within the interior of the lower bellows 19. This valve plunger is in alignment with a valve seat 32 formed in the threaded bushing 19a. It will be seen that a fire, spark or explosion occurring within the housing 11 is prevented from escaping through 3 bore 22 to the outside of the speaker since any pressure developed in the housing from such a cause would tend to compress the bellows and close the valve.

The construction shown in Fig. 2 is similar to that shown in Fig. 1, however, in this instance the voice coil 18 and the speaker cone 24 are linked by a rigid shaft 33 axially movable in bore 35 and extending at each end beyond the core 14.

The upper portion of shaft 33 projects through a flexible bellows 23a affixed to the upper end of the soft iron core and is threaded to receive a nut 36 for securing the apex of the speaker cone to the shaft for movement therewith.

A disc shaped coil support 37 threaded onto the lower end of shaft 33 supports voice coil 18a in magnetic flux gap 17.

Threaded into the lower end of housing 11 is a substantially cup-shaped closure 40 having a threaded extension 41 adapted to receive a suitable explosion proof conduit coupling (not shown) through which may pass the voice coil leadin wires.

In the embodiment shown in Fig. 2 the safety valve comprises a valve face portion 38 formed integral with disc 37 and movable upwardly to cooperate with the valve seat 39 formed in the lower end of iron core 14.

Thus, should an explosion occur within the housing cavity the resulting flame could not escape to the outside atmosphere for the pressure on the undersurface of support 37 would tend to move valve face 38 into sealing engagement with valve seat 39 closing bore 35.

In some installations it may be desirable to locate the electrical unit of the transducer at a distance from the hazardous atmosphere, as behind a Wall of the room where the hazardous conditions are present, or in a room adjacent thereto. Such an arrangement is shown in Fig. 3, where, it will be noted, the sealed housing 11 containing the electrical elements is secured to the outer face of a wall partition 44 and the speaker cone assembly is secured to the outer face of such opposite wall partition 45. The arrangement is similar to the embodiment illustrated in Fig. 1 but includes a fluid conduit 42 of the required length extending through the wall or partition and around corners if necessary to connect the voice coil bellows 19 and the speaker bellows 23.

As shown such a construction may include an auxiliary plate 43 afllxed to the wall 41 as by threaded screws to provide a suitable mounting base for the speaker cone housing 25 and flexible bellows 23 as shown.

If housing 11 is located a distance from the speaker cone unit, conduit 42 may consist of two sections of tubing one of the sections being threaded into soft iron core 14 and the other section threadedly connected to flexible bellows 23. The sections may be joined by a suitable coupling (not shown) and a bleed valve may be inserted in the fluid line if desired.

It will be apparent from the foregoing description that the present invention may be used with particular advantage not only in hazardous areas but also wherever the atmospheric conditions are such that dust, dirt or moisture might enter the area surrounding the electrical elements and thus interfere with the efi'lcient operation of the transducer.

Although the embodiment which has been illustrated and described herein relates to the application of the invention to transducers of the permanent magnet type, it is to be understood that it is not intended to limit the invention to that particular type of transducer. For it will be apparent to those skilled in the art that the invention broadly includes a novel linkage arrangement for connecting acoustical and electrical elements and for sealing such constructions.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. 'In a transducer containing a voice coil, a speaker diaphragm and a magnetic core therebetween, said core having a bore therethrough, a shaft extending through said bore to connect said coil and said diaphragm, a valve face portion carried by said shaft on the coil side of said transducer, and said magnetic core having a valve seat formed therein around the bore on the coil side thereof for cooperation with said valve face portion to seal said bore.

2. In a transducer containing a voice coil, a speaker diaphragm and amagnetic core therebetween, said core having a bore therethrough, a shaft extending through said bore to connect said coil and said diaphragm, a valve face portion carried bysaid shaft on the coil side of said transducer, a valve seat formed around the bore on the coil side of said magnetic core for cooperation with said valve face portion to seal said bore, and a discshaped coil support intgeral with said valve face portion and threadedly engaged to said shaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,743,194 Deane Jan. 14, 1930 1,744,032 Baldwin Ian. 21, 1930 1,808,149 Smith June 2, 1931 2,069,242 Graham Feb. 2, 1937 

